A comprehensive research study is proposed that will evaluate the following two hypotheses. First, the absorbed dose to individual radiosensitive organs within pediatric and adult medical patients can be directly assessed using anatomically-realistic reference computational phantoms. Second, uncertainties in these patient organ doses can be both quantified and reduced through the use of Non-Uniform Rational B-Spline (or NURBS) based computational phantoms uniquely sculpted to match individual patient body morphometry. In Aim 1 of the project, two reference computational phantoms of the adult male and adult female will be constructed according to their definition in Publication 89 of the International Commission on Radiological Protection (ICRP). Aim 2 will then involve free-form deformation of these phantoms to permit modeling of individual patients with total weights and/or heights that either exceed or are below their 50th percentile values as given in CDC health statistical data. Techniques for expansion or contraction of outer body contour of the phantoms are already established in our laboratory, and thus provide for patient-specific adjustments to skeletal muscle and subcutaneous fat. CT image data will be collected and analyzed regarding distributional patterns of intra-abdominal fat, and their impact on organ-to-organ positioning in adult male and female patients. Aim 3 will expand existing simulations algorithms in our laboratory for helical CT scanning, to include non-uniform source weighting as relevant to mA modulation techniques of modern-day scanners. Finally, Aim 4 will launch a series of patient-specific dose reconstructions of adult patients undergoing CT imaging. Individual organ doses will be assessed using a series of increasing patient-specific reference phantoms (stylized, voxel, hybrid, hybrid trunk-height-matched, and finally hybrid patient-sculpted). These doses will be compared to those from a gold-standard voxel phantom segmented from the patient's own CT images, a task that will rarely be performed clinically. The results of the latter study will be used to test our research hypotheses and to provide statistical data regarding the level of patient specificity necessary to achieve given levels of dosimetry accuracy. The overall effort will provide the technological basis for a CT organ dose tracking system in diagnostic radiology, and for substantial improvements in dose reconstruction methods applied to either prospective or retrospective radiation epidemiological studies. [unreadable] [unreadable] [unreadable]